Biosynthesis and characterization of bacterial cellulose synthesized by Komagataeibacter sp. using agri-food byproducts as cost-effective substrates

Biosynthesis and characterization of bacterial cellulose synthesized by Komagataeibacter sp. using agri-food byproducts as cost-effective substrates Joel Armando Njieukama, Lorenzo Sirolia,b, Marianna Cicconea, Giacomo Braschia,b, Davide Gottardia,b, Paulo Jose do Amaral Sobralc, Francesca Patrignania,b, and Rosalba Lanciottia,b a Department of Agricultural and Food Science, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Piazza Goidanich 60, Cesena (FC), Italy b Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum, University of Bologna, Campus of Food Science, Via Quinto Bucci 336, Cesena (FC), Italy c Faculty of Animal Science and Food Engineering (FZEA-USP), R. Duque de Caxias, 225 - Pirassununga Brasile Bacterial cellulose (BC) is a commercially valuable biopolymer renowned for its high purity, mechanical strength, and nanofibrillar structure. However, the economic feasibility of large-scale BC production is constrained by the high cost of conventional culture media. This study explores the biosynthesis and physicochemical characterization of BC produced by Komagataeibacter xylinus DSM 2004 and Komagataeibacter rhaeticus LM4 using beet molasses (BM) and brewer's spent grains (BSG) as cost-effective carbon and nitrogen sources. After a 10-day fermentation at 28°C under static conditions, BC yield, cell load, sugar consumption and gluconic acid production were evaluated. The resulting BC films were characterized via Fouriertransform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and the mechanical properties were assessed. The results show that DSM 2004 exhibited superior BC production, yielding 3.11 g/L in BM medium and 1.55 g/L in BSG medium, whereas K. rhaeticus LM4 produced 1.80 g/L and 1.46 g/L of cellulose, respectively. Both bacterial strains demonstrated good growth kinetics, with incomplete sugar utilization. The sodium phosphate buffer used efficiently mitigated possible decrease of pH during the fermentation. However, an increase in pH was observed in BM medium inoculated with DSM 2004 due to the consumption of gluconic acid previously produced. The variability in BC yields resulted in significant variability in thickness (0.0100-0.0392 mm) which correlated with the mechanical properties. DSM 2004-derived BC from BM medium demonstrated the highest tensile strength (127.55 MPa) and Young’s modulus (49.91 MPa), albeit with low elongation at break (4.95 %). Hydrophilic behaviour was observed in LM4-derived BC, while DSM 2004-derived BC displayed unexpected hydrophobicity. FTIR spectra confirmed cellulose I structure across all samples, while XRD revealed crystallinity differences, with the highest crystallinity index observed in DSM 2004-produced BC from BM medium. These results underscore the potential of BM and BSG as sustainable, low-cost substrates for efficient BC production, aligning with circular bioeconomy principles and waste valorisation strategies.